There are known lens-replacement type camera systems where an imaging apparatus, which is the camera main body, performs imaging processing and lens control, and lens devices which are interchangeable lenses perform lens driving in accordance with control commands from the camera main body. In such camera systems, transmission of control commands from the camera main body to the interchangeable lens, and transmission of lens information from the interchangeable lens to the camera main body, are performed via a communication channel for exchanging information with each other.
Of such lens-replacement type camera systems, digital camera systems in particular require smooth lens control in accordance with imaging cycles when shooting moving images or taking live view images. Accordingly, the imaging timing of the camera main body and the control timing of the interchangeable lens need to be synchronized, and the camera main body needs to complete obtaining of lens information necessary for lens control and transmission of control commands to the interchangeable lens within an imaging cycle.
PTL 1 discloses a clock-synchronized communication system made up of three channels, which are a clock channel, a data transmission channel from the camera main body to the interchangeable lens, and a data transmission channel from the interchangeable lens to the camera main body. In this communication system, the camera main body serves as a communication master to generate clock signals, and outputs one frame of clock signals to the interchangeable lens via the clock channel. The interchangeable lens and the camera main body then exchange information synchronized with the clock signals.
However, in the communication system according to PTL 1, the interchangeable lens serving as a communication slave cannot communicate data to the camera main body unless it receives a transmission request signal from the camera main body serving as the communication master.
PTL 2 discloses an imaging system where the communication method is changed to an asynchronous communication method, and where information indicating that data communication will be performed can be transmitted from the interchangeable lens to the camera main body via the channel used as the clock channel in clock-synchronized communication.